1. Field of the Invention
The present invention relates to a calender with a roll stack that has two end rolls and at least one intermediary roll, wherein the end rolls each have a deflection compensation device that acts in the direction of the intermediary roll.
2. Discussion of Background Information
In the current state of the art, calenders are frequently embodied as supercalenders. Supercalenders have a large number of rolls, as a rule 10 or 12, that are disposed vertically one above another. The end rolls are disposed in the highest and lowest positions. The end rolls may also be called the top roll and the bottom roll, respectively.
Calenders of this kind are used, for example, for satinating a paper web, i.e., the paper web is conducted through the nips between neighboring rolls. Through suitable means, the rolls are placed against one another with pressure. This treatment on the one hand compresses the paper web and on the other, gives it an improved surface quality, e.g., higher gloss or better smoothness. The pressing can take place in either of two ways: in the first, one of the two end rolls rotates at a fixed location and the other roll is pressed by a pressing means, e.g., a hydraulic cylinder, in the direction of the fixed end roll; in the second, the top roll and the bottom roll have pressing means that act in opposite directions. The deflections thus produced can be compensated for by deflection compensation devices so that all nips assume a straight course.
At this point, paper manufacturers often like to carry out a matte satination. The process of matte satination may be carried out by a soft calender. Soft calenders, however, are often not available as a result of cost or space requirements, so that the supercalender has to additionally take care of this function.
To carry out matte satination in conventional supercalenders, one of the rolls that is supported in vertically movable supports is fastened in its position in the roll stack using a suitable mechanical locking means. As a rule, the roll fastened in its position is one of the intermediary rolls. All the vertically movable rolls disposed beneath it, including the bottom roll, which is embodied as a deflection compensation roll, are pressed upward against the locked roller by means of a hydraulic cylinder. The deflection of the rolls is in turn compensated for by a deflection compensation device of the bottom roll.
This process has some disadvantages. Frequently, the roll disposed directly above the bottom roll cannot be locked so that a number of rolls, which do not contribute directly to the satination process, have to be driven and correspondingly undergo wear and tear. More importantly, the satination pressure is not adjustable as a practical matter. The satination pressure can only be so great that the deflection of the individual rolls is corrected. In other words, the pressing force of the currently functioning rolls can only be as great as is permitted by the compensation of the individual load deflection of the locked center roll. The pressing force is therefore determined by the weight, the width, and the rigidity of the locked center roll. The pressing force in the working nip cannot be changed because this would lead to an asymmetry of the pressure on the roll width and result in a distortion of the rolled material. If the pressure is too great, the locked roll deflects upward. However, if the pressure is too small, then the locked roll deflects downward.